# Kinetic energy

Kinetic energy is the energy an object has because of its motion.

• Planets, cars, people and atoms all have kinetic energy due to their motion.
• When a force is applied to an object, its kinetic energy can change.
• Kinetic energy is the energy of motion, while potential energy is the energy of position or state.
• Most interactions between objects involve forces and can transfer energy.
##### Energy
• Energy is the capacity to do work. It can exist in different forms such as kinetic, potential, thermal, and electromagnetic.
• Energy cannot be created or destroyed; it can only be converted from one form to another.
• Objects at absolute zero do not have any thermal energy to transfer, but they can still interact and exchange other forms of energy.
##### Force
• Force is a term used to describe the interaction between objects that causes a change in motion or shape.
• Galaxies, human beings and electrons can all apply forces to the things around them.
• Work is defined as the product of the force applied on an object and the distance it moves in the direction of the force.
##### At an atomic scale
• Electrical energy passes through a circuit as electrons flow, transferring their kinetic energy to other electrons in the circuit.
• Heat is produced as photons strike an object, transferring their energy to electrons within the atoms or molecules of its surface.
##### At a human scale
• The human senses of sight, hearing, and touch are tuned to respond to different forms of energy when a force interacts with our bodies.
• When a person hears a sound or sees something, that is evidence of energy having been transferred to their senses.
• So when a person sees something, it is evidence of energy having been transferred to their senses through forces like light waves.
• The fact that light waves exist and travel through space is evidence of the electromagnetic force without which electromagnetic waves wouldn’t be possible.
• The amount of energy carried by the light wave is directly related to the perceived brightness of an object.
• This means that the intensity (or amount of energy) carried by these light waves determines how bright the object appears to us.
• The stronger the electromagnetic force acting on the source of the light (like a star or a light bulb), the more energy the light waves carry and the brighter the object appears.
##### Here is another example
• A person pushes a heavy boulder up a hill.
• Each time they push they apply force to make the boulder move.
• They feel exhausted by the time they reach the top because of the work involved in overcoming the force of gravity and friction.
• But the energy is not lost, instead, it is transferred to the boulder as kinetic energy.
• As soon as the boulder is released and starts to roll back down the hills, the kinetic energy it has gained is transferred to other boulders it crashes into.
• If the boulder is too heavy to move, no work is done on the boulder. However, the person’s muscles still expend energy, which is released into the environment as heat.
###### References
• Kinetic energy is the energy an object has because of its motion.
• Planets, cars, people and atoms all have kinetic energy due to their motion.
• When a force is applied to an object, its kinetic energy can change.
• Kinetic energy is the energy of motion, while potential energy is the energy of position or state.
• Most interactions between objects involve forces and can transfer energy.